Structural, Optical, and Electrochemical Properties of Three-Dimensional Push–Pull Corannulenes

Electrochemically active corannulene derivatives with various numbers of electron-donating 4-(<i>N,N</i>-dimethylamino)­phenylethynyl (<b>1</b>–<b>4</b>) or electron-withdrawing cyanobutadienyl peripheral substitutents (<b>5</b>–<b>8</b>) were prepared. The latter derivatives resulted from formal [2 + 2] cycloaddition of cyanoolefins to <b>1</b>–<b>4</b> followed by retro-electrocyclization. Conformational properties were examined by variable-temperature NMR and X-ray diffraction and opto-electronic properties by electronic absorption/emission spectra and electrochemical measurements; these analyses were corroborated by dispersion-corrected density functional calculations at the level of B97-D/def2-TZVPP. In CH₂Cl₂, <b>1</b>–<b>4</b> exhibit intramolecular charge-transfer (ICT) absorptions at 350–550 nm and green (λ_em ∼ 540 nm) or orange (600 nm) fluorescence with high quantum yields (56–98%) and are more readily reduced than corannulene by up to 490 mV. The variation of optical gap and redox potentials of <b>1</b>–<b>4</b> does not correlate with the number of substituents. Cyanobutadienyl corannulenes <b>5</b>–<b>8</b> show red-shifted ICT absorptions with end-absorptions approaching 800 nm. Intersubstituent interactions lead to distortions of the corannulene core and lower the molecular symmetry. NMR, X-ray, and computational studies on <b>5</b> and <b>8</b> with one cyanobutadienyl substituent suggested the formation of intermolecular corannulene dimers. Bowl-inversion barriers around Δ<i>G</i>^⧧ = 10–11 kcal/mol were determined for these two molecules